Honestly, I can't assume that benadryl WILL mask anaphylaxis. It certainly never has with DD.
If that argument held any water at all, it would be a problem for the thousands of allergic people who are on maintenance antihistamines. It's not.
It's like a seawall-- it'll hold out a high tide, but not a hurricane surge. It's not like not having it there makes things "better" or more noticeable, actually.
One problem that I saw as potentially problematic here is that this was a classic fatal reaction; no cutaneous symptoms, and only VERY vague, really subjective symptoms until she was just a few minutes from death when the really overt (and all grade IV+) stuff started and snowballed. That is what kills teens and young adults, actually. They lose some of the "classic" allergy symptoms that are grade II and III-- and if those are things that they and their families have come to regard as litmus tests for "is this a reaction?" then they have to be in VERY serious trouble before they realize that they are dealing with in-progress anaphylaxis. Another thing that surprises people is just how FAST it can happen. I can't emphasize that enough. Fatal reactions can be fast. Breathtakingly fast. It's surreal.
No hives doesn't mean no reaction.
Benadryl is irrelevent to that, actually. DD hasn't reliably manifested hives with anything but minor (contact) reactions since she was about 7yo. She also doesn't always have audible wheezing. But she's had blood pressure crashes, which are just as capable of killing.
I've known at least 30 different people to do exactly what this family did-- that is, wait-and-see after a possible small ingestion (remember, the report is that she spit it out and rinsed her mouth). Only about five of them even paid for it with a trip to the emergency room, and only one of those children required more than ER care for a few hours. None of them died. I literally have only known ONE person in all my years with FAS to have administered epi after a probable ingestion-- but with NO symptoms.
As for remote and non-ideal hospital conditions, well... welcome to the West. I can name on my two hands the number of places it'd be "okay" to anaphylax out here west of the Mississippi. If you're away from a population center (and geographically, that's a lot of us), then you're going to have a non-ideal hospital experience. On the other hand, there are less-than-stellar emergency rooms in cities, too.
I know exactly how this happened. I just know it. This girl asked someone in a dimly lit room "what are those?" and someone answered her-- "Oh, they're just rice krispie treats." So she took one. Simple misunderstanding-- maybe not something that an adult would have misjudged-- but at 13, I could very easily see my DD doing it with the prepackaged ones, at least. I'm pretty sure that there is no way that she'd have eaten something that was home-made. But other people do it all the time.